Such devices pertinent to the general background of the present invention, often known as thread brakes, are well known in many different conventional configurations and arrangements, and are typically used, for example, as weft thread brakes in weaving looms.
German Patent 34 46 567 and corresponding U.S. Pat. No. 4,641,688 disclose a weft thread brake with a controllable braking effect. This known weft thread brake comprises two lamellar brake elements that are arranged opposite each other and press against each other in a spring-elastic manner, with the weft thread received therebetween. The known thread brake arrangement further comprises at least one controllable electromagnetic actuator that selectively acts on and moves or applies a force to at least one of the lamellar brake elements relative to the other, and thereby causes an adjustable braking force to be applied to the thread passing between the two lamellar brake elements.
A similar embodiment and construction of a weft thread brake is known from German Patent 43 06 911 and corresponding U.S. Pat. No. 5,398,731. The basic construction of this known thread brake also includes two lamellar brake elements that selectively or adjustably press against each other, with the weft thread passing therebetween. The position and force of at least one of the lamellar brake elements relative to the other is adjustable by means of a stepper motor, and an actuating cam element that is mounted eccentrically on the shaft of the stepper motor, so that the actuating cam variably acts on the lamellar brake elements due to the stepping rotation of the stepper motor.
A great number and variety of other types of thread brakes are generally known in the art of textile processing machines. For example, some known thread brakes operate with a brake band and a controllable brake body, with the weft thread guided therebetween, for example according to European Patent 0,475,892. Another type of thread brake involves a so-called thread looping or wrapping brake, in which the thread is deflected, looped, or wrapped to a variable extent around a braking element, and the applied braking force is adjustable by changing the thread deflection or looping angle. The basic principle of such a brake arrangement is described in connection with the thread tensioning apparatus in European Patent Specification 0,467,059.
In all of the known apparatuses in this context, the overall thread brake arrangement essentially consists of the actual thread break device itself together with an additional thread tension sensor. Namely, the thread tension is measured by an additional or separate thread tension sensor in order to then control the actuation of the thread brake in response to and dependent on the measured thread tension. Unfortunately, in all of the known arrangements, the separate thread tension sensor requires the thread to be deflected around a suitable measuring element in order to be able to measure the actual presently existing thread tension, which is representative of or associated with the applied braking force. In this manner, a force proportional to the actual existing thread tension is exerted onto the suitable measuring element, which then provides a signal representative of the thread tension.
The use of such a thread tension sensing arrangement is disadvantageous, because the necessary additional deflection of the thread also causes an additional mechanical loading of the thread, which is undesirable and unnecessary. This is especially evident when it is considered that this additional deflection and loading of the thread by the tension sensing arrangement also arises even when the thread brake is not operating, i.e. when the brake is fully opened to allow the thread to pass therethrough without any braking effect.